BACKGROUND AND PURPOSE:3DRA is considered the reference standard for the assessment of intracranial aneurysm morphology. However, it has been shown that 3DRA may overestimate neck size compared with 2D DSA. The purpose of this study was to determine the impact of neck size overestimation with 3DRA on intra-aneurysmal hemodynamics.MATERIALS AND METHODS:In a series of 20 patients, 20 intracranial aneurysms were analyzed for aneurysm neck size overestimation with 3DRA compared with 2D DSA. 3DRA-derived vascular models were modified to agree with 2D DSA. Geometric and hemodynamic variables of the original and modified vascular models were compared.RESULTS:In 8 of the 20 evaluated cases, 3DRA-derived aneurysm models showed neck size overestimation compared with 2D DSA images. The average neck diameter reduction after modification was 19%, which was, on average, 0.85 mm (±0.32 mm). Modification of the neck resulted in differences in location of inflow jet (2/8), impingement zone (3/8), and low WSS area (4/8). In 1 case, the maximal WSS increased by 98% after modification. The change of impingement zone location resulted in a different classification of the impingement zone region in 2 cases.CONCLUSIONS:Neck size overestimation on 3DRA can have non-negligible consequences for hemodynamic features determined with CFD.